Be more verbose when we can't clean up a mountpoint
left over from an earlier run.
Check in a much smaller BOOT.BIN.gz.  Remove boot.scr.  Tweak fstab for
faster operation.  Add ntp to rc.conf.  Modify setup.sh for compressed
BOOT.BIN.
Include KERNCONF=<kernconf> in /etc/src.conf so that
"make buildkernel" and "make installkernel" will Just Work
on the built system.
Use the new U-Boot-beaglebone port if it's installed.
Merge branch 'skibo-master'